This invention relates to methods for making salts of hydroxy-substituted alkyl or aromatic hydrocarbons. In one particular embodiment the invention relates to the preparation of alkali metal salts of hydroxy-substituted alkyl or aromatic hydrocarbons.
Salts of hydroxy-substituted hydrocarbons are frequently required for synthesis of hydroxy-substituted hydrocarbon derivatives or for use as bases in chemical reactions to name just two of their many uses. For example, salts of hydroxy-substituted aromatic hydrocarbons (sometimes referred to as phenate salts) are frequently required for synthesis of hydroxy-substituted aromatic hydrocarbon derivatives. In some embodiments salts of dihydroxy-substituted aromatic hydrocarbons are used in the preparation of monomers for use in condensation polymerization to form polymers with structural units derived from said dihydroxy-substituted aromatic hydrocarbons. For example, alkali metal salts of dihydroxy-substituted aromatic hydrocarbons may be employed in displacement reactions with appropriately substituted phthalimides to prepare monomers for use in synthesis of polyetherimides. Salts of dihydroxy-substituted aromatic hydrocarbons may also be used themselves as monomers in condensation polymerization. For example, alkali metal salts of dihydroxy-substituted aromatic hydrocarbons may participate in polymerization reactions with appropriately substituted aromatic bis(substituted phthalimide)s to prepare polyetherimides directly. In particular examples U.S. Pat. No. 5,229,482 discloses a displacement method for the preparation of polyetherimides from bis(chlorophthalimides) and alkali metal salts of dihydroxy-substituted aromatic hydrocarbons using a solvent of low polarity such as o-dichlorobenzene in the presence of a thermally stable phase transfer catalyst such as a hexaalkylguanidinium halide. U.S. Pat. No. 5,830,974 discloses a similar method using a monoalkoxybenzene such as anisole as solvent. These methods made it possible for the first time to envision the commercial production of polyetherimides and other condensation polymers by a displacement method. Nevertheless, several problems remain to be solved for the optimum development of the displacement reaction for condensation polymer preparation. In particular a reliable method is needed for synthesis of alkali metal salts of hydroxy-substituted hydrocarbons and particularly hydroxy-substituted aromatic hydrocarbons on a large scale.
U.S. Pat. No. 4,520,204 describes the manufacture of salts such as bisphenol A disodium salt by forming the salt in an aqueous solution with sodium hydroxide and adding the aqueous solution to refluxing ortho-dichlorobenzene with removal of water to afford a salt slurry. The salt slurry in organic solvent is further dried by refluxing over calcium hydride or by azeotropic removal of water with an organic solvent. The procedure is problematic in that foaming may occur during the addition of the aqueous salt solution to the refluxing ortho-dichlorobenzene.
U.S. Pat. No. 4,546,207 describes the manufacture of anhydrous salts of dihydroxyaromatic compounds by forming the salt in an aqueous solution with excess sodium hydroxide and then isolating the solid salt from the reaction mixture. The solid salt is then treated with an organic solvent and the mixture evaporated to dry the salt. In this procedure the salt may be obtained as a hydrate with varying degree of hydration making it difficult to do stoichiometry calculation in subsequent reactions.